I am retrofitting a new CT/X-Ray feeder in a doctors clinic. There is an existing 200amp feeder to a 208-WYE/480-DELTA, step-up transformer. The 480v output is feeding a 100amp fusible disco fused at 90amp. When I opened the transformer there is no ground connection to either winding. There is a #6 green coming from the MDP along with 3/0 power conductors. This EGC is landed on the frame lug and continues on with the #2 conductors to the equipment disco. There is no neutral load. My question is do I just corner ground the DELTA winding with a properly sized EGC coming from MDP? Does that conductor also serve as the GEC. 
